How do I use the Curve Profile > Helix (3D)
It is indeed a bit strange that one can't enter a number of twists or revolutions in the Curve Profiles menu. There are workarounds:
Method 1:
Simply duplicate the curve in Edit Mode, move it along the z axis (where the distance is the height of the curve) and delete the bottom vertex of the top curve. Then select the vertices you want to bridge and press F.

Method 2:
Turn your curve into a mesh (Alt + C by default, and choose Mesh from Curve/Meta/Surf/Text) so you can more easily make certain changes. Apply a Array modifier (with the Merge box checked) for instance.

Then after the changes are made to the mesh, turn the object back into a curve. (Alt + C again, and choose Curve from Mesh/Text)

But it might be a different kind of curve now. We can fix that by setting the spline type.
You can do this by pressing the search hotkey (usually F3 or Spacebar) and search for the command &quot;Set Spline Type&quot;, and choose for instance Bezier.

Lastly you could select all vertices and change the Handle Type, for instance to Aligned. Now you can have the same kind of curve you started out with, only (most probably) with more vertices than before.

If the curve is a Bezier and you want to reduce the number of vertices in the curve, you can do Decimate Curve and enter a value between 0 and 1.